The Aerosol In-Situ Laboratory is dedicated to the long-term observation of near-surface aerosol properties, both physical and chemical, originating from natural and anthropogenic sources. It plays a central role in understanding pollutant composition and dynamics, particularly focusing on components such as black carbon, organic aerosols, and secondary inorganic species. These observations contribute to assessing air quality and evaluating potential health impacts. The ACTRIS-related instrumentation has been in continuous operation at the RADO-Bucharest site since early 2020, following strict calibration and quality assurance protocols. The laboratory is equipped with advanced instruments including an Aethalometer, Aerosol Chemical Speciation Monitor (ACSM), Cloud Condensation Nuclei Counter (CCN counter), Aerodynamic Particle Sizer (APS), Scanning Mobility Particle Sizer (SMPS), Nephelometer, and Condensation Particle Counter (CPC). On the outdoor measurement platform, a GRIMM EDM 180 optical particle counter (OPC) and a Rapid-E bioaerosol detector are also in continuous use, enabling comprehensive particle characterization across size, composition, and biological origin. A characteristic diurnal pattern in aerosol concentrations is regularly observed, with peaks linked to human activity and atmospheric dynamics such as boundary layer height. Seasonal trends reveal increased contributions from residential heating and biomass burning during colder months, while summer periods are generally marked by lower aerosol loadings and improved dispersion. By combining continuous measurements with source apportionment techniques, the laboratory provides critical insights into urban aerosol sources and trends. Its integration into the ACTRIS research infrastructure ensures that high-quality, standardized data support national and European air quality assessments.